So, let’s get this one out of the way right off the bat. Litmus is one of the biggest names in email testing, and this tool is used by most enterprise-level operations. 

Generally speaking, Litmus can help you preview your emails on a wide variety of platforms, and you can change code right in the platform. Litmus is, in fact, so successful that it has acquired other email testing tools, such as PutsMail.

At MailPoet, we use Litmus nearly every week as part of our Quality Assurance step to ensure our email templates look good on every email client, including mobile.